The present invention relates to methods of forming rivet joints.
Rivets and methods of joining metal sheets together employing rivets have been known for many years, and involve inserting a rivet into aligned holes drilled through the sheets followed by deforming the rivet by compression so that it expands radially on either side of the sheets and holds them together. Where access to only one side of the sheets is easily available, it is usual to employ a blind rivet for forming the joint. A typical blind rivet comprises a sleeve formed from the rivet material that is located about a mandrel having an enlarged head at one end. Usually the mandrel extends some distance beyond the other end of the rivet sleeve as a pulling stem, and a radially extending flange is provided on the end of the rivet sleeve opposite to the mandrel head. In addition, a point of weakness called a breakneck may be provided in the mandrel in the region of the rivet sleeve. The blind rivet can be inserted through the hole formed in the sheets to be joined beginning with the head of the mandrel until the flange on the rivet sleeve abuts the surface of the sheet on the working side thereof so that only the head of the mandrel and part of the rivet sleeve are located on the blind side of the sheets. The rivet can then be set by means of a rivet setting tool which grasps the pulling stem of the rivet and pulls it away from the proximal end of the rivet sleeve while applying a reaction force to the flanged end of the sleeve. This causes the head of the mandrel to be drawn toward the sleeve and the sleeve to be compressed between the head of the mandrel and the rivet setting tool. The setting tool will apply a sufficient force to deform the rivet sleeve axially, and therefore radially, so that the set rivet will hold the sheets together. After setting of the rivet, the mandrel may be snapped in two at the breakneck and the remainder of the pulling stem can be discarded. The head of the mandrel and any part adjacent to it may be removed and discarded so that only the deformed rivet sleeve remains, although in some circumstances it may be left in the sleeve. Thus, in order to grip the sheets and hold them together, some volume of rivet sleeve material is required to remain on each outwardly directed surface of the metal sheets, this being provided by the flange on one side of the sheets.
This form of riveting has been considered for joining parts of the chassis or housing of an electronics assembly. Such a chassis or housing that has been employed is in the form of a container formed from sheet metal such as pressed aluminium zinc plated steel and having a number of internal, generally rectangular areas for receiving various components, for instances power modules, printed circuit boards, disc, tape and CD-ROM drives etc. Space is normally at a premium in such assemblies and various components will usually be inserted by sliding rectangular modules into the appropriate recesses with no more than one or two millimeters of tolerance. It is not economically feasible to join the various sheets forming the internal and external walls of the housing by spot welding because this would require re-plating of the steel sheets after welding. Also, it is not possible to employ usual rivets in such an assembly because this would require access to both sides of the sheets to be joined by a relatively large “l” shaped anvil of a setting tool.
Accordingly it has been considered to employ blind rivets for joining the various metal sheets forming the chassis of the equipment. However the formation of protuberances on both surfaces of the sheets to be joined by the rivets is not compatible with the requirement to be able to slide the various components into and out of the chassis, nor is it compatible with the proximity of various joined metal sheets forming internal partitions or bulkheads to other parts of the chassis.